That’s what researchers from the U.S. Forest Service and the University of Pennsylvania found in a recently published study comparing crime in ash borer infested areas to non-infested areas in Cincinnati.

Cincinnati removed 646 trees between 2007 and 2014 due to ash borer infestation, according to the study. Areas that had trees removed experienced higher crime rates than non-infested areas. Specifically, the loss of trees was associated with a “significant” increase in property crime, like burglary or vandalism. Ash borer infested blocks had, on average, six more property crimes per year than non-infested areas, the study said.

Trees have a clear impact on crime in urban areas, said Michelle Kondo, a research scientist with the U.S. Forest Service and co-author of the study.

“Evidence is showing that the loss of trees play a role in crimes at the street level,” Kondo said. “Something systematic is occurring.”

What the researchers could not conclude was why crime increased in these areas. One explanation may be that trees and vegetation create more foot traffic in a neighborhood and deter criminals, said Seunghoon Han, a criminologist at the University of Nebraska Omaha and another study co-author.

“When we make a place more ‘green’ like a park, then people spend more time walking around,” Han said. “Criminals will know there will be more surveillance.”

Another explanation for the increase in crime is called the Routine Activity Theory, Han said. It argues that a crime needs three things to take place: a likely offender, a suitable target and the absence of a capable guardian like a police officer. Trees may offer evidence of a capable guardian nearby and thus prevent crime, Han said.

“In making a place green, via trees or vegetation, criminals are more likely to think a capable guardian is nearby because of more foot traffic,” Han said. “This can deter people from developing criminal behaviors.”

Because of their impact on crime, officials in cities must consider alternatives for removing dying trees, according to Ohio State University horticulture Professor Joe Boggs.

“Maybe more budgets need to be put in to taking them down and replanting as opposed to just removing them,” Boggs said. “Whether you choose to treat or remove trees, you need to run environmental and economic impact reports.”

To assess their value, the nonprofit organization Casey Trees created the National Tree Benefit Calculator. The calculator examines things trees may affect, like stormwater run-off and air quality, to show how much trees are worth to communities. For example, one ash tree in downtown Cincinnati increases property values and reduce carbon dioxide to the tune of $79 in annual benefits to the city, according to the calculator.

Adding trees and vegetation is a simple yet effective way to improve inner cities, Han said.

“Turning problematic spaces into green spaces can change environmental factors to decrease crime and increase property values,” Han said. “Greening a place is an easy option, but the potential effect could be huge.”

Commentary

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